The present invention relates to a method of manufacturing semiconductor devices, and more particularly, to a method of forming an isolation structure of a flash memory device.
In general, as the size of a flash memory device shrinks, it is required that the depth of the isolation structure of the cell region be set different from those of the peri-region in the formation process of the isolation structure.
In the process of forming the isolation structures of the cell region and the peri region, which have different depths, a high density plasma (HDP) oxide layer is generally used as an insulating layer for trench gap-fill. This is done to prevent gap-fill failure in the trench of the cell region, which has a smaller opening than that of the trench of the peri region. A wet etch-deposition method is also used.
If the wet etch process is performed on the trench of the peri region, which has a depth deeper than that of the trench of the cell region, neighboring gate oxide layers may also be removed when the deposited insulating layer is stripped. This degrades the reliability of the device.